Accessing the controlling terminal

If a process attempts to access its controlling terminal after it has been deallocated, access is denied. If the process is not holding or ignoring SIGHUP, it is sent a SIGHUP signal. Otherwise, the access fails with an EIO error.

Members of background process-groups have limited access to their controlling terminals:

• If the background process is ignoring or holding the SIGTTIN signal or is a member of an orphaned process-group, an attempt to read from the controlling terminal fails with an EIO error. Otherwise, the process is sent a SIGTTIN signal, which by default stops the process.

• If the process is attempting to write to the terminal and if the terminal's TOSTOP flag is clear, the process is allowed access.

  The TOSTOP flag is set on reception of an M_SETOPTS message with the SO_TOSTOP flag set in the so_flags field. It is cleared on reception of an M_SETOPTS message with the SO_TONSTOP flag set.

• If the terminal's TOSTOP flag is set and a background process is attempting to write to the terminal, the write succeeds if the process is ignoring or holding SIGTTOU. Otherwise, the process stops except when it is a member of an orphaned process-group, in which case, it is denied access to the terminal and it is returned an EIO error.

• If a background process is attempting to perform a destructive ioctl (an ioctl that modifies terminal parameters), the ioctl call succeeds if the process is ignoring or holding SIGTTOU. Otherwise, the process will stop except when the process is a member of the orphaned process-group. In that case, the access to the terminal is denied and an EIO error is returned.